1. Technical Field
The present invention relates to an electrophotographic image receiving sheet having excellent low temperature fixing property and excellent adhesion resistance, capable of forming a highly glossy and high-quality image similar to that of silver halide photography, and an image forming method using the electrophotographic image receiving sheet, which exhibits excellent passing performance in a fixing device, and can prevent occurrence of running failure such as jam, double feed in an image forming apparatus.
2. Background Art
Since electrophotography, which is a dry processing, is excellent in printing speed and able to output an image on general-use paper such as plain paper and fine paper, it has been widely used in copiers and output devices used in personal computers.
Recently, in order to achieve high image quality in electrophotography, which quality is similar to that of silver halide photography, when image information of face, landscape and the like is output as a photograph, an electrophotographic image receiving sheet has been used as paper for exclusive use. Such electrophotographic image receiving sheet includes at least a toner image receiving layer formed on a support, and the toner image receiving layer is formed, for example, by a method in which a thermoplastic-resin containing composition is melted and extruded on the support so as to form a lamination thereon, a method in which a thermoplastic-resin containing coating solution is coated on the support or the like.
Thermoplastic resins used for the toner image receiving layer usually include amorphous polymers, the glass transition temperature (Tg) of which is higher than an environmental temperature and in a temperature range lower by several dozen degrees than a toner fixable temperature. These amorphous polymers are excellent in adhesiveness to toner but are also high in adhesive force between toner image receiving layers containing the toner. Thus, there is a problem that in the case where a toner image receiving layer of an electrophotographic image receiving sheet faces and superposes a back surface of another electrophotographic image receiving sheet during storage and transportation thereof, the toner image receiving layer of the electrophotographic image receiving sheet adheres to the back surface of another electrophotographic image receiving sheet, causing running failure such as jam, double feed, and the like.
On the other hand, crystalline polymers have low adhesive force even when the glass transition temperature (Tg) thereof is in a temperature range of below-zero, and the adhesion failure between the toner image receiving layer of one electrophotographic image receiving sheet and the back surface of another electrophotographic image receiving sheet does not occur. However, there is a problem that the crystalline polymers have insufficient adherence to toner, causing toner removal from the toner image receiving layers on which the toner has been fixed.
In order to solve the problem, there has been proposed an electrophotographic image receiving sheet in which, for example, a toner image receiving layer contains a mixture of a linear amorphous polymer with a linear crystalline polymer, a glass transition temperature (Tg1 (° C.)) of the linear amorphous polymer is 40° C. to 120° C. and a melting point (Tm (° C.)) of the linear crystalline polymer is 100° C. to 200° C. (see Patent Literature 1).
Further, there has been proposed an electrophotographic image receiving sheet in which a toner image receiving layer contains a mixture of a linear amorphous polymer with a linear crystalline polymer, and a glass transition temperature (Tg1) of the linear amorphous polymer and a melting point (Tm) of the linear crystalline polymer satisfy the relation of the following formula: (Tg1−20° C.)≦Tm≦(Tg1+20° C.), and also the Tg1 is in a range from 40° C. to 120° C. (see Patent Literature 2).
According to these proposals, it is possible to solve the problems of amorphous polymers and crystalline polymers, and to achieve both favorable toner fixing property and excellent adhesion resistance, thereby forming a highly glossy and high-quality image.
However, in these proposals, a solution prepared by dissolving the mixture of the linear amorphous polymer with the linear crystalline polymer in an organic solvent is used, causing a serious impact on the environment. Further, in the above proposals, a highly glossy image is obtained when a fixing temperature is high, for example, approximately 155° C. However, when the fixing temperature is lowered, there occur defects such as a decreased gloss and uneven gloss occurring on a boundary line between an image portion and a non-image portion. Therefore, when the fixing temperature is lowered for the purpose of saving energy, only an unpleasant image is obtained which is inferior in uniformity. Moreover, all of these prior arts disclose the toner image receiving layers having single layer structures, and it has been difficult to satisfy both excellent low temperature fixing property and excellent adhesion resistance in the toner image receiving layers having single layer structures.
There has also been proposed a medium to be transferred for a color electrophotographic image having a toner image receiving layer formed of a crystalline polyester resin in which an aromatic dicarboxylic acid component is contained as an acid-derived component and straight-chain aliphatic diol, bisphenol S, or bisphenol S alkylene oxide additive is contained as an alcohol derived component (see Patent Literature 3).
Moreover, there has been proposed an image support material in which a thermoplastic resin of a toner image receiving layer is formed of a polyester resin prepared by melting and mixing a crystalline polyester resin and an amorphous polyester resin and a viscosity of 103 Pa·s is obtained at a temperature from 80° C. to 110° C. (see Patent Literature 4).
However, in these proposals, there is a problem that the toner image receiving layers have single layer structures, and are hard to satisfy both excellent low temperature fixing property and excellent adhesion resistance, and that the toner image receiving layer is not formed by a coating method but is formed by a melt extrusion method, which requires expensive production facilities and an increased quantity of energy, resulting in an increased production cost, a greater impact on the environment and a poor quality of the gloss.
Under these circumstances, there has not yet been provided an electrophotographic image receiving sheet having a satisfiable performance, such as excellent low temperature fixing property and excellent adhesion resistance, capable of forming a highly glossy and high-quality image similar to that of silver halide photography, and an image forming method using the electrophotographic image receiving sheet, which exhibits excellent passing performance in a fixing device, and can prevent occurrence of running failure such as jam, double feed in an image forming apparatus. At present, the prompt provision thereof is demanded.    Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 2005-181881    Patent Literature 2: JP-A No. 2005-181883    Patent Literature 3: JP-A No. 2005-92097    Patent Literature 4: JP-A No. 2005-99123